IL-10- and TGF-β-driven BCL6 expression suppresses antiviral defenses and renders lymph node T follicular helper cells permissive to HIV infection

Lymph nodes (LNs) constitute a key anatomical sanctuary for HIV. Follicular helper T (Tfh) cells expand early upon infection and represent a principal cellular target for initial viral seeding. Here, we identified the transcription factor BCL6, a Tfh-lineage defining marker, as central in favoring the infection of Tfh cells in LNs during the untreated phase in humans, and for the persistence of the reservoir during ART in non-human primates. In situ and ex vivo analyses of LN from people with HIV (PWH) in absence of antiretroviral therapy (ART) revealed preferential enrichment of viral RNA, total HIV DNA, and intact proviruses within BCL6hi Tfh cells, which also presented significantly lower expression of proteins with antiviral functions (IRF7, MX1, APOBEC3G, pSTAT1). In vitro genetic (genome-wide CRISPR knockouts) and pharmacologic perturbations confirmed that BCL6 enhances the cellular permissiveness of Tfh cells to HIV infection. IL-10 and TGF-β were enriched in LNs from people without HIV (PWoH), and cooperatively induced bona fide BCL6hi Tfh differentiation in vitro, with repressed antiviral pathways. IL-10 and TGF-β blockade limited Tfh differentiation, confirming their contribution to Tfh and LN biology. Human Single Nucleotide Polymorphisms (SNPs) in proximity to genes of the IL-10 and TGF-β pathways were enriched in PWH who controls viremia spontaneously (HIV elite controllers). Importantly, in vivo downmodulation of IL-10 and TGF-β signaling pathways in ART-treated SIV-infected macaques, by using anti–IL-10 and anti–PD-1 therapy, led to reduced frequencies of LN BCL6+ Tfh cells. These Tfh cells expressed significantly higher expression of antiviral machineries, similar to gene signatures found in HIV elite controllers, and resulted in significantly lower SIV reservoir size in LNs. This data highlights that the modulation of the IL-10/TGF-β/BCL6 axis is relevant at early stages upon infection, but also during ART, after the HIV reservoir is already established. In both scenarios it results in higher antiviral machinery and lower HIV seeding and reservoir sizes. Thus, the modulation of these pathways in vivo has potential to alter Tfh biology in LNs leading to HIV reservoir decay, contributing to HIV cure strategies.